Mutual assured destruction (MAD) is the doctrine of a situation in which any use of nuclear weapons by either of two opposing sides would result in the destruction of both the attacker and the defender. The doctrine assumes that each side has enough weaponry to destroy the other side and that either side, if attacked for any reason by the other, would retaliate with equal or greater force. The expected result is that the battle would escalate to the point where each side brought about the other's total and assured destruction - and, potentially, those of allies as well.

Assuming that neither side would be so irrational as to risk its own destruction, neither side would dare to launch a first strike as the other would launch on warning[?] (also called fail deadly). The payoff of this doctrine was expected to be tense but stable peace.

The primary application of this doctrine occurred during the Cold War (1950s to 1990s) between the United States and Soviet Union, in which MAD was seen as helping to prevent any direct full-scale conflicts between the two nations while they engaged in smaller proxy wars around the world.
MAD was part of U.S. strategic doctrine which believed that nuclear war between the Soviet Union and the United States could best be prevented if neither side could defend itself against the other's nuclear missiles (see Anti-Ballistic Missile Treaty). The credibility of the threat being critical to such assurance, each side had to invest substantial capital in weapons, even those not intended for use.

This MAD scenario was often known by the less frightening euphemism "nuclear deterrence".

Critics of the MAD doctrine noted that the acronym MAD fits the word mad (meaning insane, as in "mad as a hatter"), and the doctrine was satirized in the 1964 film Dr. Strangelove or, How I Learned to Stop Worrying and Love the Bomb. In the film, the Soviets have a doomsday machine which automatically detects any nuclear attack on the Soviet Union, whereupon it destroys all life on earth by fallout. The film mirrored life in that the nuclear strategist Herman Kahn had actually contemplated such a machine as one strategy in ensuring mutual assured destruction.

The fall of the Soviet Union has reduced tensions between Russia and the United States and between the United States and China. MAD has been replaced as a model for stability between Russia and the United States as well as between the United States and China. Although the administration of George W. Bush has abrogated the anti-ballistic missile treaty, the limited national missile defense system proposed by the Bush administration is designed to prevent nuclear blackmail by a state with limited nuclear capability and is not planned to alter the nuclear posture between Russia and the United States. MAD's replacement (asymmetric warfare) is designed to take advantage of years of analysis that focussed on finding a concept for stability that did not rely on holding civilian populations hostage.

The Bush administration has approached Russia with the idea of moving away from MAD to a different nuclear policy of total weaponry escalation. Russia has thus far been rather unreceptive to these approaches largely out of fear that a different defense posture would be more advantageous to the United States than to Russia.

Some argue that MAD was abandoned on 25 July1980 when US President Jimmy Carter adopted the countervailing strategy in Presidential Directive 59. From this date US policy was to win a nuclear war. The planned response to a Soviet attack was no longer to bomb Russian cities and assure their destruction. American nuclear weapons were first to kill the Soviet leadership, then attack military targets, in the hope of a Russian surrender before total destruction of the USSR (and the USA). This policy was further developed by President Ronald Reagan with the announcement of the Strategic Defense Initiative (aka Star Wars), aimed at destroying Russian missiles before they reached the US. If SDI had been operational it would have undermined the "assured destruction" required for MAD.